Hey there!
I can totally relate to what you're going through right now, and I wanna let you know that it's totally normal. It doesn't mean your lazy or a bad person, it's completely normal to feel a bit melancholic and tired all the time when everything is in complete lockdown and things seem to be running at about half the speed they normally are.
Firstly, careful with energy tablets. They're not really gonna help you feel more motivated, and even if they make you less tired temporarily, they'll make up for it later but tiring you out as your brain recovers. Plus they'll slowly lose their effect. They're not exactly dangerous of course, but not a good idea to rely on them if you're tired all the time. If you're tired, make sure you're giving yourself the time to get at least 9 hours of sleep (or at least really try to), and if you still feel tired to the point where it affects you, or you can't sleep properly, then just talk to your doctor! People have sleep and tiredness problems all the time.
As for motivation, the best thing to do is to sit down and promise yourself you'll do some work. Get up, put some actual clothes on, and then really try to do an hour of work or so. If you find yourself getting distracted, just try and focus back. EVEN if you can only manage half an hour then that's okay, take a lil break and come back. Keep going outside (although not in ur PJ's silly) as that really helps to refresh you, as does eating properly. If you just try and slowly build up the amount of work you do every day, you'll begin to feel much more motivated and ready to work.
And hey, if you really feel like you can't work because you're too tired and unmotivated or maybe even depressed, please don't be afraid to talk to your doctor, or any other mental health professional or support. You don't have to have a severe mental health issue to talk to a doctor or counsellor, and even if you think your issue is relatively trivial, they might be able to help you if you think you can't do it on your own.
Hope that helps <3